Wide-angle: the Achilles' heel of SLRs?

Discussion in '35mm Cameras and Accessories' started by David Lyga, Nov 18, 2012.

  1. David Lyga

    David Lyga Subscriber

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    Because of the inability to place the rear element closer to the film plane (the mirror gets in the way) RFs are touted as having superior wide-angle results. We know that this is so in theory and that compromises had (and still have?) to be made with optical formulas in order to 'compensate and correct'.

    But, I ask, is this still so, with computer technology determining, most efficiently, the lens formulas of today? In other words, is a top flight Nikon wide angle (say 20, 24, of 28) inferior in any way to a Leica RF lens of the same focal length? - David Lyga
     
  2. AgX

    AgX Member

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    As you indicated hat mirror issue made it neccesary to exchange a classic wide-angle design for a retro-focus design, probably introducing additional abberations.

    Nonwithstanding any achievements in retro-focus desings on which you inquire, the retro-focus principle lets the imaging rays fall onto the film with steaper angles than with the classic concept, thus the cosines-law will have less effect. Thus no need for a correcting density filter and by that a virtual speed gain of such lenses.
     
  3. illumiquest

    illumiquest Member

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    If a 4000$ Leica 21mm isn't better than a 650$ Nikon 20mm...
     
  4. David Lyga

    David Lyga Subscriber

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    AgX: So, (in my mathematical ignorance) does that mean that the 'steeper angles' forgo the need to worry about the edges being less exposed? In terms of resolution, however, is this retro-focus compromise just as good? (Hope that I made at least some sense!) - David Lyga
     
  5. Mark Crabtree

    Mark Crabtree Member

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    I thought this would be about the difficulty focusing wide angles on slrs. That is the Achilles' heel of slrs to me, and also the place rangefinders really shine.

    For the rest, I'm in agreement with AgX that the retrofocus design can offer some advantages. Still, there are trade offs. The best modern slr wide angles are supposedly fabulous, but are generally much larger than I would want. Rangefinder lenses are usually a much smaller package.

    BTW, many rangefinder lenses shorter than 35 are retrofocus too, but still shorter than slrs. Leica started doing that in the 70's, I think, to allow clearance for metering.
     
  6. Ian Grant

    Ian Grant Subscriber

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    It's not so much the price rather the design and there's no way of matching the quality of a pure wide angle lens with a retro focus SLR WA design.

    A better example although MF not 35mm would be a comparison of the 38mm Biogon on the Hassleblad SWC with the 40mm Distagon for the regular Hasselblads.

    Ian
     
  7. David Lyga

    David Lyga Subscriber

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    Very interesting how retro-focus can actually be an advantage.

    Perhaps there will be others with relevant comments on this topic. All I have ever heard is how 'compromised' the SLR wide-angles are but I see nothing but sensational results from such 'inferiority'.

    Mark Crabtree: you are very correct to state that focusing them is a problem with SLRs but some are better than others. - David Lyga
     
  8. AgX

    AgX Member

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    Yes David, that was what I meant.

    At the Leica-Camera website you'll find pdf's with MTF's for both classic and retro-focus wide-angle lenses. Perhaps they'll make you wiser concerning resolution.

    EDIT:
    Refering to the subsequent postings, you'll also find there graphics concerning distorsion.
     
    Last edited by a moderator: Nov 18, 2012
  9. Mark Crabtree

    Mark Crabtree Member

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    That's true. I've used some pretty good finders, but they are still dependent on the lens speed. I'm happy with my 35 f2.8 Distagon, but not with focusing it indoors. With a Leica, or similar, that isn't a factor.
     
  10. markbarendt

    markbarendt Subscriber

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    David,

    As far the WA's I've used on my Nikons, all I can say is that it would be highly doubtful that simply substituting Leica gear would have "improved" anything.

    I'm not saying a lab could not find something to measure, just that that difference would not have made a significant change in the success of the photos.

    A $4000 Leica Lens is definitely better at being "jewelry". :whistling:
     
  11. markbarendt

    markbarendt Subscriber

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    I agree that SLRs can provide a struggle with focus in low light, the advantage for the rangefinder here lies in the body/rangefinder mechanism not being affected by the lens brightness, right?
     
  12. David Lyga

    David Lyga Subscriber

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    Of course, given the outrageously generous depth of field with wide-angles, you really could 'range focus' the old fashioned way and suffer nothing. - David Lyga
     
  13. Ian Grant

    Ian Grant Subscriber

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    Unless you've used a pure wide-angle lens it's hard to appreciate the differences, there's less of the exaggerated pulling effects at the edges of a similar SLR lens, it's less distorted.

    I use the equivalent of a 21mm Leica lens on my 5x4 camera and in most of the images you wouldn't realise how wide angle a lens I'd used. In the early 1990's I used a 21mm on my Leica for a few months and was extremely impressed with the lens.

    Ian
     
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  15. georg16nik

    georg16nik Member

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    David, as far as I know there are physical limits in the SLR land and so far big sized lenses with compromises is the only way to go.
    What Ian Grant wrote about Biogon and Distagon in the Hassy is a good way to look at it.

    In RF land, it was not until 1935 when Michail Russinov (or Roosinov) pioneered the use of aberration vignetting (to improve corner illumination) and designed vignetting filter deposited on the inner surface of the wide angle objective exterior lens..
    Also, M.M Russinov pioneered the idea of enlarging the size of the entrance pupil as angular coverage increases..
    By 1946 M.M.Russinov lens design (Russar) was patented and documented widely.
    Zeiss and Leitz came late to the game and that explains why they used workarounds.

    When Ludwig Bertele was commissioned by Zeiss in 1951 to design a wide angle lens for Contax and Hasselblad, Bertele could not obtain master patent for the use of single meniscus at each end of the lens as Russinov had already covered this.

    At the International Congress at Stockholm in 1956 Ludwig Bertele paid tribute to Russinov for his highly interesting and original solution to the problem of securing adequate illumination in the picture corners etc. etc..

    In 2011 Dr. Hubert Nasse, senior scientist at Zeiss and chief optical designer wrote in Camera Lens News 41 published by Zeiss Carl Zeiss AG Camera Lens Division:
     
  16. michael_r

    michael_r Subscriber

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    Retrofocus wide angles can be made just as sharp and well corrected for certain aberrations as RF lenses, but they require significantly more complex designs and usually many more elements (which in the past could have led to reduced contrast but is not currently much of an issue. In theory aspheric elements take the place of several spherical elements in the correction of things like spherical aberration.

    For me, the Achilles' heel of retrofocus wides is geometric distortion. By definition a retrofocus (reverse telephoto) lens is not symmetrical, which introduces geometric distortion, which is complicated and expensive to correct. As a result while many RF wides exhibit minimal and/or virtually invisible amounts of barrel distortion, a partially corrected but still very visible amount of simple barrel or complex (mustache) distortion is usually considered a good performance even in a $2,000+ SLR wide. There are a few exceptions around, but generally it seems to me most new SLR prime wide designs are pretty lackluster when it comes to geometric distortion correction. My guess is that is because most people are shooting digital and simple geometric distortion can be largely corrected post-capture. Unfortunately while there are some very sharp SLR wides, in my experience the correlation between price and distortion correction is relatively weak.
     
  17. MikeTime

    MikeTime Member

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    No complaints about the 2.8/24 and 2.8/28 Ai-S's; great '80's lenses. But then, maybe they're not real wide angles...
     
  18. Mark Crabtree

    Mark Crabtree Member

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    I've been wanting a 21 Super Angulon for some time. Normally I don't shoot that wide, but I really enjoy that lens. Maybe it has something to do with the characteristics you mention. With lenses, I sure like some more than others, but often can't attribute it to a particular characteristic.

    The Nikkor 24 f2.8 was a very good lens for the time, and one I still like. I imagine shooting it side by side with a Super Angulon would show up some significant differences.

    And, of course, that doesn't mean your pictures would be better with a better lens, but that wasn't the question here.
     
  19. Diapositivo

    Diapositivo Subscriber

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    I am not a lens design expert but would agree with the theory that wherever there is some additional constraints in lens design, either price or lens quality has to suffer, or both.

    I have a small and quite well made Voigtländer 15mm on my Voigtländer Bessa-L and the pair is light, portable, and fairly inexpensive.
    A 15mm on a SLR would undoubtedly be more expensive, heavier, and very likely sacrifice some image quality on the altar of design complexity. I very often take pictures of architectural subjects so distortion correction is something I deeply like.

    I would say that, overall, wide-angle photography is something that would better be left at range-finders. If you are the kind of persons that goes around with two or three bodies, the wide-angle body should be a range-finder (or quasi range-finder, like a Contax G2). It's not just a matter of distortion correction but also a matter of weight and size.
     
  20. Bill Burk

    Bill Burk Subscriber

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    Enjoyed the lens design story, thanks georg16nik.

    As several have noted... In terms of ease of focus and composition... rangefinders are well suited to wide angle, while SLR's are better suited to telephoto.
     
  21. semi-ambivalent

    semi-ambivalent Subscriber

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    Michael,

    In the late 70s a "teacher" at the traveling Nikon School said wide angles don't have distortion but exaggerated perspective. He followed with a sensible proof using the ratio of distance to foreground objects and distance to background objects. Whether or not this was provided to explain away true distortion in WA Nikkors versus WAs by Leitz I don't know but 1) It made perfect sense, and 2) I've never had much problem with "distortion" if I framed the image correctly. Usually, I was after the FG/BG thing so I coaxed it as much as I could. And, with the Nikkor Retros I could actually afford the 28s, 24s and 20s that let me get the images I was after. If Leitz was the only source of wide angles I doubt I would have ever picked up a camera. I have no doubt the geometries and optics can affect things here but must also think at least some of the spiel behind $3k 35s is to explain away Leica's antiquated production workflow.
     
  22. AgX

    AgX Member

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    The terminology on these matters is vague.

    I would distinguish between:

    -) perspective distortion

    -) geometric distortion

    -) lens distortion

    I admit that these terms too are ambiguous.
     
  23. semi-ambivalent

    semi-ambivalent Subscriber

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    Bill,

    I've never had a problem focusing a (Nikon) WA. One must only pull the split prism to the point you want focused and turn the camera a bit, if necessary, to get some angle across the split. Focus, compose and done. This works for me down to f/3.5, the slowest WA I have (28mm non-Ai). I'm 58 so we'll see what my eyes have to say about this going forward. Additionally an RF, unless I use an external viewfinder, does not show me the 'distortion' a WA provides, only its FOV, an SLR cannot avoid showing both. I am often after just that and it helps composition to be able to see it.

    Having the muscle memory to pull that split prism around, now that I own an M3 one would think it would be easy to remember that I have to pull that split image around too. But I'm having a hell of a time remembering that when things are moving fast (My kingdom for a ground glass!). This might help explain the popularity of 35mm lenses for RFs; the DOF makes it easier to go all HCB on it.

    s-a
     
  24. Diapositivo

    Diapositivo Subscriber

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    "Distortion" is a lens defect. Some people use the term "geometric distortion" to express the typical wide-angle perspective. Some other people call that wide-angle perspective "distortion" but that really is incorrect IMO. The teacher was probably explaining them that that is not "distortion" but has a geometrical - optical explanation and is, therefore, unavoidable and perfectly normal.

    That said, wide angles have distortion proper just like any other lenses.
     
  25. michael_r

    michael_r Subscriber

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    I am referring specifically to geometric distortion, not wide angle perspective "stretching". The distortion I refer to is the failure of the lens to form a true rectilinear image due to asymmetry and the position of the diaphragm. These compromises cause either barrel distortion (straight lines "bow" outward, most visible along the edges of the frame), pincushion distortion (the opposite of barrel) or complex distortion (a combination of barrel and pincushion - typically barrel transitioning to pincushion toward the corners, hence the term "mustache" often used to describe it). Generally in retrofocus lenses barrel distortion is the common defect while pincushion distortion usually affects telephoto designs (to a lesser degree) although either type of distortion (or both) can be present in both long and short focal lengths.

    Wide angle RF lenses typically suffer significantly less barrel distortion than SLR retrofocus wides.
     
  26. Bill Burk

    Bill Burk Subscriber

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    semi-ambivalent,

    I guess I too never have any real "problem" focusing wide angle with an SLR. And I also have no trouble focusing a 90mm with M2... It's just that it seems relatively easier (since focus patch is the same for any lens) to focus the rangefinder with wide angle...